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//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This family of functions perform manipulations on basic blocks, and
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// instructions contained within basic blocks.
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Constant.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/ValueHandle.h"
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/// DeleteDeadBlock - Delete the specified block, which must have no
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void llvm::DeleteDeadBlock(BasicBlock *BB) {
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assert((pred_begin(BB) == pred_end(BB) ||
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// Can delete self loop.
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BB->getSinglePredecessor() == BB) && "Block is not dead!");
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TerminatorInst *BBTerm = BB->getTerminator();
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// Loop through all of our successors and make sure they know that one
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// of their predecessors is going away.
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for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i)
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BBTerm->getSuccessor(i)->removePredecessor(BB);
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// Zap all the instructions in the block.
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while (!BB->empty()) {
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Instruction &I = BB->back();
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// If this instruction is used, replace uses with an arbitrary value.
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// Because control flow can't get here, we don't care what we replace the
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// value with. Note that since this block is unreachable, and all values
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// contained within it must dominate their uses, that all uses will
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// eventually be removed (they are themselves dead).
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I.replaceAllUsesWith(UndefValue::get(I.getType()));
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BB->getInstList().pop_back();
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BB->eraseFromParent();
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/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are
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/// any single-entry PHI nodes in it, fold them away. This handles the case
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/// when all entries to the PHI nodes in a block are guaranteed equal, such as
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/// when the block has exactly one predecessor.
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void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
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while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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if (PN->getIncomingValue(0) != PN)
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PN->replaceAllUsesWith(PN->getIncomingValue(0));
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PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
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PN->eraseFromParent();
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/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
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/// is dead. Also recursively delete any operands that become dead as
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/// a result. This includes tracing the def-use list from the PHI to see if
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/// it is ultimately unused or if it reaches an unused cycle.
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bool llvm::DeleteDeadPHIs(BasicBlock *BB) {
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// Recursively deleting a PHI may cause multiple PHIs to be deleted
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// or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
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SmallVector<WeakVH, 8> PHIs;
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for (BasicBlock::iterator I = BB->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I)
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for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
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if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
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Changed |= RecursivelyDeleteDeadPHINode(PN);
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/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
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/// if possible. The return value indicates success or failure.
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bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
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pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
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// Can't merge the entry block. Don't merge away blocks who have their
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// address taken: this is a bug if the predecessor block is the entry node
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// (because we'd end up taking the address of the entry) and undesirable in
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if (pred_begin(BB) == pred_end(BB) ||
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BB->hasAddressTaken()) return false;
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BasicBlock *PredBB = *PI++;
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for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
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PredBB = 0; // There are multiple different predecessors...
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// Can't merge if there are multiple predecessors.
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if (!PredBB) return false;
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// Don't break self-loops.
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if (PredBB == BB) return false;
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// Don't break invokes.
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if (isa<InvokeInst>(PredBB->getTerminator())) return false;
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succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
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BasicBlock* OnlySucc = BB;
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for (; SI != SE; ++SI)
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if (*SI != OnlySucc) {
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OnlySucc = 0; // There are multiple distinct successors!
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// Can't merge if there are multiple successors.
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if (!OnlySucc) return false;
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// Can't merge if there is PHI loop.
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for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
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if (PHINode *PN = dyn_cast<PHINode>(BI)) {
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == PN)
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// Begin by getting rid of unneeded PHIs.
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while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
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PN->replaceAllUsesWith(PN->getIncomingValue(0));
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BB->getInstList().pop_front(); // Delete the phi node...
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// Delete the unconditional branch from the predecessor...
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PredBB->getInstList().pop_back();
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// Move all definitions in the successor to the predecessor...
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PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
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// Make all PHI nodes that referred to BB now refer to Pred as their
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BB->replaceAllUsesWith(PredBB);
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// Inherit predecessors name if it exists.
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if (!PredBB->hasName())
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PredBB->takeName(BB);
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// Finally, erase the old block and update dominator info.
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if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) {
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DomTreeNode* DTN = DT->getNode(BB);
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DomTreeNode* PredDTN = DT->getNode(PredBB);
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SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
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for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(),
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DE = Children.end(); DI != DE; ++DI)
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DT->changeImmediateDominator(*DI, PredDTN);
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BB->eraseFromParent();
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/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
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/// with a value, then remove and delete the original instruction.
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void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
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BasicBlock::iterator &BI, Value *V) {
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Instruction &I = *BI;
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// Replaces all of the uses of the instruction with uses of the value
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I.replaceAllUsesWith(V);
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// Make sure to propagate a name if there is one already.
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if (I.hasName() && !V->hasName())
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// Delete the unnecessary instruction now...
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/// ReplaceInstWithInst - Replace the instruction specified by BI with the
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/// instruction specified by I. The original instruction is deleted and BI is
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/// updated to point to the new instruction.
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void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
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BasicBlock::iterator &BI, Instruction *I) {
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assert(I->getParent() == 0 &&
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"ReplaceInstWithInst: Instruction already inserted into basic block!");
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// Insert the new instruction into the basic block...
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BasicBlock::iterator New = BIL.insert(BI, I);
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// Replace all uses of the old instruction, and delete it.
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ReplaceInstWithValue(BIL, BI, I);
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// Move BI back to point to the newly inserted instruction
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/// ReplaceInstWithInst - Replace the instruction specified by From with the
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/// instruction specified by To.
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void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
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BasicBlock::iterator BI(From);
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ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
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/// RemoveSuccessor - Change the specified terminator instruction such that its
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/// successor SuccNum no longer exists. Because this reduces the outgoing
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/// degree of the current basic block, the actual terminator instruction itself
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/// may have to be changed. In the case where the last successor of the block
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/// is deleted, a return instruction is inserted in its place which can cause a
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/// surprising change in program behavior if it is not expected.
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void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) {
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assert(SuccNum < TI->getNumSuccessors() &&
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"Trying to remove a nonexistant successor!");
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// If our old successor block contains any PHI nodes, remove the entry in the
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// PHI nodes that comes from this branch...
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BasicBlock *BB = TI->getParent();
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TI->getSuccessor(SuccNum)->removePredecessor(BB);
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TerminatorInst *NewTI = 0;
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switch (TI->getOpcode()) {
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case Instruction::Br:
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// If this is a conditional branch... convert to unconditional branch.
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if (TI->getNumSuccessors() == 2) {
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cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum));
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} else { // Otherwise convert to a return instruction...
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// Create a value to return... if the function doesn't return null...
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if (!BB->getParent()->getReturnType()->isVoidTy())
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RetVal = Constant::getNullValue(BB->getParent()->getReturnType());
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// Create the return...
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NewTI = ReturnInst::Create(TI->getContext(), RetVal);
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case Instruction::Invoke: // Should convert to call
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case Instruction::Switch: // Should remove entry
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case Instruction::Ret: // Cannot happen, has no successors!
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llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!");
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if (NewTI) // If it's a different instruction, replace.
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ReplaceInstWithInst(TI, NewTI);
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/// GetSuccessorNumber - Search for the specified successor of basic block BB
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/// and return its position in the terminator instruction's list of
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/// successors. It is an error to call this with a block that is not a
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unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) {
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TerminatorInst *Term = BB->getTerminator();
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unsigned e = Term->getNumSuccessors();
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for (unsigned i = 0; ; ++i) {
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assert(i != e && "Didn't find edge?");
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if (Term->getSuccessor(i) == Succ)
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/// SplitEdge - Split the edge connecting specified block. Pass P must
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BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
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unsigned SuccNum = GetSuccessorNumber(BB, Succ);
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// If this is a critical edge, let SplitCriticalEdge do it.
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TerminatorInst *LatchTerm = BB->getTerminator();
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if (SplitCriticalEdge(LatchTerm, SuccNum, P))
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return LatchTerm->getSuccessor(SuccNum);
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// If the edge isn't critical, then BB has a single successor or Succ has a
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// single pred. Split the block.
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BasicBlock::iterator SplitPoint;
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if (BasicBlock *SP = Succ->getSinglePredecessor()) {
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// If the successor only has a single pred, split the top of the successor
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assert(SP == BB && "CFG broken");
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return SplitBlock(Succ, Succ->begin(), P);
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// Otherwise, if BB has a single successor, split it at the bottom of the
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assert(BB->getTerminator()->getNumSuccessors() == 1 &&
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"Should have a single succ!");
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return SplitBlock(BB, BB->getTerminator(), P);
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/// SplitBlock - Split the specified block at the specified instruction - every
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/// thing before SplitPt stays in Old and everything starting with SplitPt moves
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/// to a new block. The two blocks are joined by an unconditional branch and
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/// the loop info is updated.
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BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
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BasicBlock::iterator SplitIt = SplitPt;
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while (isa<PHINode>(SplitIt))
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BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
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// The new block lives in whichever loop the old one did. This preserves
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// LCSSA as well, because we force the split point to be after any PHI nodes.
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if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>())
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if (Loop *L = LI->getLoopFor(Old))
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L->addBasicBlockToLoop(New, LI->getBase());
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if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>())
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// Old dominates New. New node domiantes all other nodes dominated by Old.
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DomTreeNode *OldNode = DT->getNode(Old);
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std::vector<DomTreeNode *> Children;
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for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
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Children.push_back(*I);
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DomTreeNode *NewNode = DT->addNewBlock(New,Old);
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for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
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E = Children.end(); I != E; ++I)
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DT->changeImmediateDominator(*I, NewNode);
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if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>())
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/// SplitBlockPredecessors - This method transforms BB by introducing a new
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/// basic block into the function, and moving some of the predecessors of BB to
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/// be predecessors of the new block. The new predecessors are indicated by the
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/// Preds array, which has NumPreds elements in it. The new block is given a
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/// suffix of 'Suffix'.
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/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
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/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
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/// In particular, it does not preserve LoopSimplify (because it's
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/// complicated to handle the case where one of the edges being split
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/// is an exit of a loop with other exits).
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BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
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BasicBlock *const *Preds,
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unsigned NumPreds, const char *Suffix,
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// Create new basic block, insert right before the original block.
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BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
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BB->getParent(), BB);
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// The new block unconditionally branches to the old block.
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BranchInst *BI = BranchInst::Create(BB, NewBB);
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LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0;
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Loop *L = LI ? LI->getLoopFor(BB) : 0;
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bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
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// Move the edges from Preds to point to NewBB instead of BB.
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// While here, if we need to preserve loop analyses, collect
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// some information about how this split will affect loops.
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bool HasLoopExit = false;
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bool IsLoopEntry = !!L;
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bool SplitMakesNewLoopHeader = false;
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for (unsigned i = 0; i != NumPreds; ++i) {
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// This is slightly more strict than necessary; the minimum requirement
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// is that there be no more than one indirectbr branching to BB. And
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// all BlockAddress uses would need to be updated.
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assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
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"Cannot split an edge from an IndirectBrInst");
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Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
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// If we need to preserve LCSSA, determine if any of
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// the preds is a loop exit.
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if (Loop *PL = LI->getLoopFor(Preds[i]))
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if (!PL->contains(BB))
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// If we need to preserve LoopInfo, note whether any of the
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// preds crosses an interesting loop boundary.
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if (L->contains(Preds[i]))
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SplitMakesNewLoopHeader = true;
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// Update dominator tree and dominator frontier if available.
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DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0;
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DT->splitBlock(NewBB);
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if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0)
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DF->splitBlock(NewBB);
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// Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
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// node becomes an incoming value for BB's phi node. However, if the Preds
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// list is empty, we need to insert dummy entries into the PHI nodes in BB to
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// account for the newly created predecessor.
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// Insert dummy values as the incoming value.
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for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
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cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
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AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
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// Add the new block to the nearest enclosing loop (and not an
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// adjacent loop). To find this, examine each of the predecessors and
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// determine which loops enclose them, and select the most-nested loop
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// which contains the loop containing the block being split.
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Loop *InnermostPredLoop = 0;
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for (unsigned i = 0; i != NumPreds; ++i)
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if (Loop *PredLoop = LI->getLoopFor(Preds[i])) {
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// Seek a loop which actually contains the block being split (to
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// avoid adjacent loops).
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while (PredLoop && !PredLoop->contains(BB))
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PredLoop = PredLoop->getParentLoop();
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// Select the most-nested of these loops which contains the block.
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PredLoop->contains(BB) &&
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(!InnermostPredLoop ||
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InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
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InnermostPredLoop = PredLoop;
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if (InnermostPredLoop)
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InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
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L->addBasicBlockToLoop(NewBB, LI->getBase());
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if (SplitMakesNewLoopHeader)
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L->moveToHeader(NewBB);
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// Otherwise, create a new PHI node in NewBB for each PHI node in BB.
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for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
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PHINode *PN = cast<PHINode>(I++);
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// Check to see if all of the values coming in are the same. If so, we
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// don't need to create a new PHI node, unless it's needed for LCSSA.
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InVal = PN->getIncomingValueForBlock(Preds[0]);
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for (unsigned i = 1; i != NumPreds; ++i)
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if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
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// If all incoming values for the new PHI would be the same, just don't
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// make a new PHI. Instead, just remove the incoming values from the old
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for (unsigned i = 0; i != NumPreds; ++i)
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PN->removeIncomingValue(Preds[i], false);
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// If the values coming into the block are not the same, we need a PHI.
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// Create the new PHI node, insert it into NewBB at the end of the block
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PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
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if (AA) AA->copyValue(PN, NewPHI);
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// Move all of the PHI values for 'Preds' to the new PHI.
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for (unsigned i = 0; i != NumPreds; ++i) {
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Value *V = PN->removeIncomingValue(Preds[i], false);
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NewPHI->addIncoming(V, Preds[i]);
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// Add an incoming value to the PHI node in the loop for the preheader
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PN->addIncoming(InVal, NewBB);
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/// FindFunctionBackedges - Analyze the specified function to find all of the
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/// loop backedges in the function and return them. This is a relatively cheap
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/// (compared to computing dominators and loop info) analysis.
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/// The output is added to Result, as pairs of <from,to> edge info.
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void llvm::FindFunctionBackedges(const Function &F,
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SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
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const BasicBlock *BB = &F.getEntryBlock();
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if (succ_begin(BB) == succ_end(BB))
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SmallPtrSet<const BasicBlock*, 8> Visited;
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SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
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SmallPtrSet<const BasicBlock*, 8> InStack;
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VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
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std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
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const BasicBlock *ParentBB = Top.first;
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succ_const_iterator &I = Top.second;
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bool FoundNew = false;
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while (I != succ_end(ParentBB)) {
542
if (Visited.insert(BB)) {
546
// Successor is in VisitStack, it's a back edge.
547
if (InStack.count(BB))
548
Result.push_back(std::make_pair(ParentBB, BB));
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// Go down one level if there is a unvisited successor.
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VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
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InStack.erase(VisitStack.pop_back_val().first);
559
} while (!VisitStack.empty());
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/// AreEquivalentAddressValues - Test if A and B will obviously have the same
567
/// value. This includes recognizing that %t0 and %t1 will have the same
568
/// value in code like this:
569
/// %t0 = getelementptr \@a, 0, 3
570
/// store i32 0, i32* %t0
571
/// %t1 = getelementptr \@a, 0, 3
572
/// %t2 = load i32* %t1
574
static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
575
// Test if the values are trivially equivalent.
576
if (A == B) return true;
578
// Test if the values come from identical arithmetic instructions.
579
// Use isIdenticalToWhenDefined instead of isIdenticalTo because
580
// this function is only used when one address use dominates the
581
// other, which means that they'll always either have the same
582
// value or one of them will have an undefined value.
583
if (isa<BinaryOperator>(A) || isa<CastInst>(A) ||
584
isa<PHINode>(A) || isa<GetElementPtrInst>(A))
585
if (const Instruction *BI = dyn_cast<Instruction>(B))
586
if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
589
// Otherwise they may not be equivalent.
593
/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the
594
/// instruction before ScanFrom) checking to see if we have the value at the
595
/// memory address *Ptr locally available within a small number of instructions.
596
/// If the value is available, return it.
598
/// If not, return the iterator for the last validated instruction that the
599
/// value would be live through. If we scanned the entire block and didn't find
600
/// something that invalidates *Ptr or provides it, ScanFrom would be left at
601
/// begin() and this returns null. ScanFrom could also be left
603
/// MaxInstsToScan specifies the maximum instructions to scan in the block. If
604
/// it is set to 0, it will scan the whole block. You can also optionally
605
/// specify an alias analysis implementation, which makes this more precise.
606
Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
607
BasicBlock::iterator &ScanFrom,
608
unsigned MaxInstsToScan,
610
if (MaxInstsToScan == 0) MaxInstsToScan = ~0U;
612
// If we're using alias analysis to disambiguate get the size of *Ptr.
613
unsigned AccessSize = 0;
615
const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType();
616
AccessSize = AA->getTypeStoreSize(AccessTy);
619
while (ScanFrom != ScanBB->begin()) {
620
// We must ignore debug info directives when counting (otherwise they
621
// would affect codegen).
622
Instruction *Inst = --ScanFrom;
623
if (isa<DbgInfoIntrinsic>(Inst))
626
// Restore ScanFrom to expected value in case next test succeeds
629
// Don't scan huge blocks.
630
if (MaxInstsToScan-- == 0) return 0;
633
// If this is a load of Ptr, the loaded value is available.
634
if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
635
if (AreEquivalentAddressValues(LI->getOperand(0), Ptr))
638
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
639
// If this is a store through Ptr, the value is available!
640
if (AreEquivalentAddressValues(SI->getOperand(1), Ptr))
641
return SI->getOperand(0);
643
// If Ptr is an alloca and this is a store to a different alloca, ignore
644
// the store. This is a trivial form of alias analysis that is important
645
// for reg2mem'd code.
646
if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) &&
647
(isa<AllocaInst>(SI->getOperand(1)) ||
648
isa<GlobalVariable>(SI->getOperand(1))))
651
// If we have alias analysis and it says the store won't modify the loaded
652
// value, ignore the store.
654
(AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
657
// Otherwise the store that may or may not alias the pointer, bail out.
662
// If this is some other instruction that may clobber Ptr, bail out.
663
if (Inst->mayWriteToMemory()) {
664
// If alias analysis claims that it really won't modify the load,
667
(AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
670
// May modify the pointer, bail out.
676
// Got to the start of the block, we didn't find it, but are done for this
added
removed
libclamav/c++/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
